1. Field of the Invention
The present invention relates to a heat generator which heats a viscous fluid by shearing, and exchanges the heat with a fluid circulating in a heat-receiving chamber in order to utilize the heat.
2. Description of the Related Art
Japanese Unexamined Patent Publication (Kokai) No. 10-217757 discloses a heat generator used as a heating device for vehicles. In this heat generator, a housing includes a heat-generating chamber and a water jacket which is a heat-receiving chamber neighboring the heat-generating chamber and permitting the cooling water which is a circulating fluid to circulate. The housing rotatably supports a drive shaft via a bearing that incorporates a shaft-sealing means, a pulley is attached to a front end of the drive shaft such that the drive shaft is driven by an engine through a belt, and a disk-like rotor is secured to a rear end of the drive shaft, by being pressed on, so as to rotate in the heat-generating chamber. Fluid-tight gaps between the wall surfaces of the heat-generating chamber and the outer surfaces of the rotor are filled with a viscous fluid such as silicone oil or the like that generates heat when the rotor is rotated.
In this heat generator incorporated in the heating device of a vehicle, the rotor rotates in the heat-generating chamber when the drive shaft is driven by the engine, and the viscous fluid generates heat due to the shearing in the fluid-tight gaps between the wall surfaces of the heat-generating chamber and the outer surfaces of the rotor. The heat is exchanged by the cooling water in the water jacket, and the cooling water that is heated is used for heating the compartment through a heating circuit.
In the above heat generator, however, the drive shaft is made of an iron-type metal having a high rigidity whereas the rotor secured to the drive shaft as a whole is made of an aluminum-type metal after taking the machinability and reduced weight into consideration. In this heat generator, therefore, when the rotor is rotated by the drive shaft so that the viscous fluid generates heat due to the shearing in the heat-generating chamber, the torque of the drive shaft is not reliably transmitted to the rotor, and slipping occurs between the drive shaft and the rotor due to a difference in the coefficient of thermal expansion between the drive shaft and the rotor, making it difficult to rotate the two together.
To cope with this point, it can be contrived to constitute a rotor by a disk-like main rotor body and a base portion fastened by rivet to the main rotor body and coupled to the drive shaft by spline as is done in the heat generator disclosed in Japanese Unexamined Patent Publication (Kokai) No. 9-323534.
In this heat generator, however, members such as rivets are necessary for securing the base portion to the main rotor body, and the increased number of parts drive up the cost of production. In this heat generator, further, since the base portion is coupled to the drive shaft by spline, the spline must be cut in the drive shaft and in the base portion, resulting in an increase in the number of the steps and again driving up the cost of production.
There can be further contrived a heat generator having a rotor which includes a main rotor body for shearing the viscous fluid made of a material having a coefficient of thermal expansion larger than that of the drive shaft, and a base portion made of a material having a coefficient of thermal expansion equal to that of the drive shaft, inserted into the main rotor body and secured to the drive shaft. This heat generator can be cheaply produced, and the drive shaft and the rotor can be reliably rotated together during the operation.
In this heat generator, however, it is obvious that a conflict exists between the ease of fabrication and the durability. That is, in this heat generator as shown in FIG. 8, a rotor 90 can be easily assembled if a base portion 90a secured to a drive shaft 92 is positioned by being contacted with a bearing device 91 which is a positioning member or, more concretely, if the base portion 90a secured to the drive shaft 92 is positioned by being contacted with an inner race 91a of the bearing device 91. In this heat generator, however, if the base portion 90a and the main rotor body 90b are formed having the same end surfaces without paying attention to the relationship between the main rotor body 90b of the rotor and the bearing device 91 or, more concretely, between the main rotor body 90b of the rotor and the inner race 91a of the bearing device 91, the main rotor body 90b thermally expands more than the base portion 90a and pushes the bearing device 91 or, more concretely, pushes the inner race 91a of the bearing device 91 in the axial direction when the viscous fluid generates heat during the operation and the internal temperature is elevated, since the main rotor body 90b is made of a material having a coefficient of thermal expansion larger than that of the base portion 90a. Due to the reaction, therefore, the main rotor body 90b may be deviated in the axial direction relative to the base portion 90a, and a deformation may take place along the boundary thereof.